The invention relates to a process and a system for machining and in particular for grinding the circumferential edge of eyeglass lenses with a machining tool, and in particular a grinding disk, a rotatable holder for an eyeglass lens blank and a device to control machining in accordance with a predetermined circumferential contour for the eyeglass lens.
Eyeglass edging machines are known in the art and in their simplest form may include a device to control grinding in accordance with a predetermined circumferential contour for the eyeglass lens represented by the shape of a template mounted on the rotatable holder and corresponding to the shape of the eyeglass frame opening into which the shaped eyeglass lens is to be inserted. If eyeglass lenses made of silicate glass are machined, diamond-coated grinding disks are used as a rule, while milling tools are often used to machine plastic lenses.
CNC-controlled eyeglass edging machines are also already known and are described, for example, in U.S. Pat. No. 4,945,684 or in European published unexamined patent specification 0 363 281. CNC-controlled eyeglass lens grinding machines, which grind the optical surfaces in addition, are described in European Patent Specification 0 061 918 and in U.S. Pat. No. 5,210,695 (published after the priority filing date of the present application).
In the CNC-controlled eyeglass lens edging machines, the circumferential contour of the eyeglass lens is available in the form of a data set which is used to control the grinding procedure in such a way that the predetermined circumferential contour of the eyeglass lens will be created.
Common to the purely mechanical and the CNC-controlled eyeglass lens grinding machines is the requirement that the insertion of the eyeglass lens blank in the holder is effected manually, which is time-consuming and which requires a certain degree of skill.
Before the eyeglass lens blank can be mounted in the rotatable holder of a conventional eyeglass lens grinding machine, the eyeglass lens blank must be fitted with a sucker or holder block, which must be positioned in accordance with the decentration values determined by the optician for the predetermined circumferential contour with reference to the optical axis of the eyeglass lens and which serves to exactly position the eyeglass lens blank in the rotatable holder and to make a connection with the rotatable holder resistant to relative rotation.
If the eyeglass lens exhibits a cylindrical or prismatic grind, then the axial orientation is also to be taken into consideration when applying the sucker or holder block and when inserting the lens blank in the rotatable holder of the eyeglass lens edging machine.
A further difficulty arises when eyeglass lenses are in the form of multi-focal lenses, since in this case the location of the close vision section with reference to the optical axis of the distant vision section must be taken into consideration.
To apply a sucker or holder block a device is used with which the eyeglass lens blank is initially oriented in accordance with the optical values, the decentration values and/or the axial orientation; then the sucker or holder block is attached to the pre-positioned eyeglass lens blank. A device of this type is described in U.S. Pat. No. 3,586,448.
It is quite apparent that this procedure is time-consuming and requires great professional skill, so that these activities can be carried out only by trained opticians. Due to the time-consuming positioning and blocking of each eyeglass lens blank, however, the output of the conventional eyeglass lens grinding machine, particularly if it is a CNC-controlled type, is low.
A loading unit at a CNC-controlled eyeglass lens edging machine known from U.S. Pat. No. 5,148,637 (published after the priority filing date of the present application) is suited only for loading exactly along the optical axis, so that the decentration values must be taken into account in the processing control program, whereby the calculation work is increased quite considerably and a very high-performance computer is required. The axial orientation where a cylindrical grind or prismatic grind is present and the location of a close vision section cannot be taken into consideration at all when using such a loading unit.